1. Field of the Invention
The present invention relates to a throttle valve drive apparatus which serves to control the opening of a throttle valve disposed in an intake passage of an internal combustion engine, and more particularly, to an apparatus which is capable of driving the throttle valve selectively by means of both an accelerator lever operated by an operator and an electronic control unit.
2. Description of the Prior Art
Hitherto, as a throttle valve controlling apparatus which serves to regulate the flow of intake air to an internal combustion engine, one that is capable of adjusting the opening of a throttle valve by both an accelerator operation system operated by an operator and an electric operation system driven by a control unit has been known as disclosed in Japanese Patent Unexamined Publication No. 58-20948 and Japanese Utility Model Unexamined Publication No. 60-180735.
This kind of apparatus comprises an actuator-side clutch by means of which an actuator of an electric operation system and a throttle valve are mechanically connected and disconnected and an accelerator-side clutch by means of which an accelerator lever and the throttle valve are mechanically connected and disconnected, and both clutches are controlled by an electronic control unit (ECU). In ordinary running, the actuator-side clutch is switched on (connected) and the accelerator lever-side clutch is switched off (disconnected) so that the throttle valve is driven by the actuator. On the other hand, in case of a trouble, e.g., when it becomes impossible to control the actuator, the actuator side clutch is switched off and the accelerator lever-side clutch is switched on so as to drive the throttle valve by means of the accelerator lever.
However, according to the aforesaid electronic throttle controlling apparatus disclosed in Japanese Patent Unexamined Publication No. 58-20948 or Japanese Utility Model Unexamined Publication No. 60-180735, since the on-off control of the two electromagnetic clutches are effected in accordance with instructions from the control unit, the number of arithmetic processes of the control unit is increased and complicate the control, with the result being that malfunction occurs easily. Further, if the two electromagnetic clutches are simultaneously controlled to be switched on and off, a noise produced at the time of the connection of the electromagnetic clutch becomes audible to a driver of a vehicle, thus giving rise to a problem that the vehicle makes noises while running.